Which of the following compounds can form a Zwitter ion ?

Options

A. Benzoic acid
B. Acetanilide
C. Aniline
D. Glycine

Explanation

To determine which of the given compounds can form a zwitterion, we need to understand the structure and characteristics of zwitterions.

### Step-by-Step Solution:

1. **Definition of Zwitterion**: A zwitterion is a molecule that has both positive and negative charges, but is overall neutral. Zwitterions are commonly found in amino acids, which contain both an amino group (-NH2) and a carboxylic acid group (-COOH).

2. **Identify the Structure of Amino Acids**: The general structure of an alpha amino acid can be represented as:
\[ \text{NH}_2\text{CHRCOOH} \]
Here, R represents the side chain which can vary among different amino acids.

3. **Behavior in Different pH Conditions**:
- **At pH < 7 (Acidic Medium)**: The carboxylic acid group is predominantly in its protonated form (-COOH), and the amino group accepts a proton to become -NH3^+. This results in a structure where there is a positive charge on the amino group and a neutral charge on the carboxylic group.
- **At pH = 7 (Neutral Medium)**: The carboxylic acid group loses a proton and becomes a carboxylate ion (-COO^-), while the amino group remains protonated (-NH3^+). This results in a zwitterion with both a positive and a negative charge.
- **At pH > 7 (Basic Medium)**: The carboxylic group remains in its deprotonated form (-COO^-), and the amino group is in its neutral form (-NH2). Here, the zwitterion form is not present.

4. **Identify the Given Compounds**: Among the options provided, we need to look for a compound that contains both an amino group and a carboxylic acid group. This is essential for zwitterion formation.

5. **Conclusion**: The only compound that fits this description is glycine (option D), which is the simplest amino acid. Its structure at neutral pH (pH = 7) can be represented as:
\[ \text{NH}_3^+\text{CH}_2\text{COO}^- \]
This confirms that glycine can form a zwitterion.

### Final Answer:
The compound that can form a zwitterion is **option D: Glycine**.